1. Field of the Invention
The present invention relates to a filler solution for an inkjet head, an inkjet head which is filled with the filler solution, and a recording apparatus having such an inkjet head.
2. Description of the Prior Art
Conventionally, an inkjet head for ejecting ink from a nozzle based on a piezo method or bubble-jet method to form an image on a recording medium has been known.
In the case where such an inkjet head or a recording apparatus including such an inkjet head is transported, e.g., in the case where it is shipped from its manufacturer, an ink passage in the inkjet head is filled with a filler solution in place of ink.
This is because if the ink passage is filled with ink, the ink can coagulates due to a change in environment during the transportation thereof so that the inkjet head can be clogged with the coagulated ink.
If the ink passage is left vacant, an air bubble can remain in the ink passage when ink is supplied to fill the vacant inkjet head, and the air bubble can cause ejection failure. For example, in the case of a piezo-type inkjet head, the ink in the ink passage is pressured by deformation of a piezoelectric element, whereby the ink is ejected from a nozzle. In the case of a bubble jet-type inkjet head, the ink in the ink passage is pressured by an air bubble which is generated by heating the ink, whereby the ink is ejected from a nozzle. In such inkjet heads, if an air bubble remains in the ink passage, a pressure exerted on the ink is absorbed due to a contraction of the remaining air bubble, and as a result, ejection failure is caused, i.e., the ink is not ejected from the nozzle.
There have already been filler agents for an inkjet head which have improved fillability into the ink passage. For example, Japanese Unexamined Patent Publication No. 9-327934 discloses a filler solution which contains triethylene glycol monomethylether and N-(β-aminoethyl)ethanolamine. Japanese Unexamined Patent Publication No. 2000-108493 discloses a filler solution which contains triethylamine, glycerol, diethyleneglycol, and water.
The filler solution supplied to fill the inkjet head is replaced by ink when use of the inkjet head is begun. When the filler solution is replaced by ink, an air bubble sometimes happens to be trapped in the ink passage. The air bubble trapped in the ink passage is generally removed from the ink passage as the filler solution (and ink) is ejected from a nozzle. Further, the air bubble trapped in the ink passage can be removed by so-called cleaning, i.e., by sucking out the ink from a nozzle of the inkjet head.
However, an air bubble trapped in the ink passage sometimes attaches to a wall which defines the ink passage (i.e., an internal surface of the inkjet head). It is difficult to remove such an air bubble attached to the wall by cleaning, so that the air bubble sometimes remains in the inkjet head even after the cleaning.
Thus, even in the case where the inkjet head is filled with a filler solution, such an air bubble remaining in the inkjet head can causes ejection failure of the ink-jet head.
Ink used in inkjet recording generally contains a colorant (dye or pigment), a humectant, and water. However, an image formed with the ink on a recording medium has poor water-resistivity. That is, when the image is exposed to water, the colorant exudes into the water.
In Japanese Unexamined Patent Publication No. 10-212439, Japanese Unexamined Patent Publication No. 11-293167, Japanese Unexamined Patent Publication No. 11-315231, and Japanese Unexamined Patent Publication No. 2000-178494, adding a hydrolyzable silane compound (organic silicon compound) to ink in order to improve the water-resistivity of an image formed with the ink on a recording medium has been proposed. When a drop of such ink containing a silane compound is adhered on a recording medium, and a water content (solvent) of the ink drop evaporates or permeates into the recording medium, the silane compound remaining on the recording medium is condensation-polymerized, and this condensation-polymerized silane compound encloses a colorant. As a result, even when the image formed on the recording medium is exposed to water, the colorant is prevented from exuding into the water.
Such water-resistant ink has a relatively high viscosity as compared with commonly-employed ink (i.e., ink not containing a hydrolyzable silane compound). Thus, when a filler solution in the inkjet head is replaced by the water-resistant ink, an air bubble is readily trapped in the ink passage, and accordingly, the air bubble readily attaches onto the internal surface of the inkjet head.
That is, in the case of employing water-resistant ink, an air bubble remains in the inkjet head more readily in comparison with a case of commonly-employed ink. As a result, the possibility of causing ejection failure of the inkjet head is increased.